This invention relates to a switching system for high DC current and more particularly to rapidly switching current from one pair of conductors to another pair of conductors utilized to produce an electromagnetic force for launching a projectile.
FIG. 1 schematically shows the prior art circuitry employed to commutate the current from an inductive energy source into a projectile rail of a direct current electromagnetic projectile launcher. The operation is as follows. A homopolar generator rotor is brought up to the required rotational speed by a prime mover (not shown) after which a make switch is closed. The kinetic energy provided by the prime mover is transferred to the rotor of the homopolar machine, which converts the kinetic energy to DC electrical energy, which is then transferred and stored in an induction coil. When a predetermined current is reached, a switching armature is released and is electromagnetically propelled past a projectile rail breech and the current is commutated to the projectile rails and the projectile armature. The switching armature is decelerated and continues to conduct current into the projectile rails accelerating the projectile armature and launching the projectile.
FIG. 2 shows the prior art breech in more detail, showing an insulating insert disposed over the breech to provide the arc start location ad a smooth rail surface for the switching armature. The armature is shown made up of sheets of conductive material, preferably copper, stacked one against another to form a bundle of sheets extending from rail to rail. Performance of this system was good and up to about 300,000 amps it successfully commutated the current into the projectile rail system in less than 100 microseconds. After each firing, it was only necessary to replace the last few copper sheets adjacent the trailing end of the switching armature as these consistently overheated and failed on the arcing side.
Among the objects of this invention are the improvement of the armature so as to preclude armature repair after each firing, to provide extended switch operation without any refurbishing, and to greatly increase the current carrying capacity of the switching system.
One method of increasing the life of the switching armature would be to make it longer, while maintaining the same size insulating strip. This would yield a decrease in the maximum armature current density, and hence a decrease in the heating rate, and a decrease in the force on the individual sheets. Consequently, the life of the armature would be increased. However, it would also increase the commutation time; that is, the time interval between the initiation of the current flow into the projectile rail and the full current flow into the projectile rail.